I am an EMT who is currently taking the PADI rescue course. I must say I nearly fell off my sofa when I saw the DVD demonstrate in water rescue breathing with a pocket mask. Maintaining a good seal with a BVM under ideal conditions requires a good deal of attention. If we have enough manpower the preference is to have 2 people managing airway and breathing; even then, the preference is to insert devices to prevent airway obstruction and achieve intubation ASAP.
It seems the main advantage (beyond barrier protection) to using the pocket mask is preventing the entry of water into the mouth and nose; correct me if I am wrong.
Concerning compressions vs respirations, here are a few reasons why continuous compressions are being suggested.
1) Studies have shown one reason people hesitate to render aid is because mouth-to-mouth puts them at risk. I read one study that said only 15% would be willing to do mouth-to-mouth. Meanwhile heart and brain tissue are going hypoxic.
2) People who don't do it every day have a helluva time finding a pulse or determining if it is absent. This wastes time, adds confusion as to how to proceed, leads to stress and errors. Meanwhile heart and brain tissue are going hypoxic.
3) A common public mis-perception is each time you compress the heart, blood circulates. This is not quite correct. The heart pumps at 60 or so bpm for a reason. It is struggling to maintain a pressure gradient. The signs and symtoms we call "shock" are the results of the body's attempt to maintain this pressure gradient. When the heart stops this pressure gradient falls to nothing. When we do compressions we need to build this gradient back up. The more proper compressions you make in a row, the higher this "perfusion pressure" gets. Every time you stop (rescue breaths, etc) the perfusion pressure plummets. You need to get into the high teens of a compression series before you are getting modest perfusion to the brain. This is assuming you are doing everything right, which you won't, because you will be scared out of your mind.